When you query a database with ColdFusion and your result set contains null values ColdFusion represents those values as an empty string. This is great as long as you're aware of it, you can just check the length of the string and if it's greater than 0 you know it isn't null and isn't empty.
The problem is what do you do when you want to insert or update a null into the database? If the value will always be null you can just hard code it like this...
However this doesn't help us in most cases where the value could contain something or it could be null. To do this we need to use the "null" attribute of the cfqueryparam tag. If the null attribute is set to false nothing happens and the value is used as normal. However if the null attribute is set to true, the value attribute is ignored and a null is sent to the database.
In this example if the length of the address passed in from the form is greater than 0 the value is used. However if the length is 0, the value is ignored and null is sent to the database.
Also note that this functionality is available in cfscript as shown below...
Sunday 7 July 2013
Sunday 2 June 2013
SQL Server 2012 Paging With OFFSET And FETCH
Please Note: If you're running a version of SQL Server earlier than 2012 this method for paging won't work. I have described a similar method for paging that works with all versions SQL Server 2005 and later here.
SQL Server 2012 provides us with the OFFSET and FETCH clause. We can use this clause to implement paging in a much easier and more readable way than in previous versions of SQL Server.
Let's use the same simple example we used in the earlier post...
And we want to view the 2nd page of a 10 record per page listing. Unlike in earlier versions of SQL Server, we don't really have to change the query at all, we just add the OFFSET and FETCH clause to the end of the query...
The above query will return records 11 to 20. There are just two things to keep in mind: The first is that to use the OFFSET and FETCH clause you have to include an ORDER BY and the second is that you can't use TOP in the same query.
Now if we want the next page, we just increase the offset by 10, the rest of the query can stay exactly the same...
And there you have it, too easy!
SQL Server 2012 provides us with the OFFSET and FETCH clause. We can use this clause to implement paging in a much easier and more readable way than in previous versions of SQL Server.
Let's use the same simple example we used in the earlier post...
And we want to view the 2nd page of a 10 record per page listing. Unlike in earlier versions of SQL Server, we don't really have to change the query at all, we just add the OFFSET and FETCH clause to the end of the query...
The above query will return records 11 to 20. There are just two things to keep in mind: The first is that to use the OFFSET and FETCH clause you have to include an ORDER BY and the second is that you can't use TOP in the same query.
Now if we want the next page, we just increase the offset by 10, the rest of the query can stay exactly the same...
And there you have it, too easy!
Sunday 26 May 2013
SQL Server Paging
Please Note: If you have SQL Server 2012 there is a slightly better built-in option available, which I have described here. The method described in this post works for all versions of SQL Server 2005 and later.
This post explains a very efficient way of retrieving pages of data from SQL Server. Rather than retrieving a whole data set and filtering it down with code when generating the display, which could become very slow given a large number of rows, we will only select the 10-20 rows you will be displaying at any one time.
Let's take the following query for example, which returns a list of all the members in the database that have a status of 1.
Let's imagine we want to to view the 2nd page of a 10 record per page listing, in other words we want the rows between 11 and 20. If we used the above query we would have the entire record set returned, then we can use our programming language of choice to loop over the 10 records we want and display them as required. Not very efficient given that this query could potentially return a very large number of records.
Luckily in SQL Server there is a way to reduce this result set to just the records you need for each request.
This query creates a Common Table Expression which selects the data we want while numbering each row using the ROW_NUMBER() function. Then we select the rows we want from the CTE by using the BETWEEN clause. This method is immensely faster than a straight up select query, especially on large data sets, making your pages load significantly faster.
This post explains a very efficient way of retrieving pages of data from SQL Server. Rather than retrieving a whole data set and filtering it down with code when generating the display, which could become very slow given a large number of rows, we will only select the 10-20 rows you will be displaying at any one time.
Let's take the following query for example, which returns a list of all the members in the database that have a status of 1.
Let's imagine we want to to view the 2nd page of a 10 record per page listing, in other words we want the rows between 11 and 20. If we used the above query we would have the entire record set returned, then we can use our programming language of choice to loop over the 10 records we want and display them as required. Not very efficient given that this query could potentially return a very large number of records.
Luckily in SQL Server there is a way to reduce this result set to just the records you need for each request.
This query creates a Common Table Expression which selects the data we want while numbering each row using the ROW_NUMBER() function. Then we select the rows we want from the CTE by using the BETWEEN clause. This method is immensely faster than a straight up select query, especially on large data sets, making your pages load significantly faster.
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